Hydrogen bond radii for the hydrogen halides and van der Waals radius of hydrogen

In this article, the effective size of hydrogen in the hydrogen halides forming hydrogen bonded complexes is estimated. The scheme proposed by Bhadane and Gadre [J. Chem. Phys. 107, 5625 (1997)] for estimating the size of hydrogen in HF is extended to the other hydrogen halides (HCl and HBr) and HCN. It is noted that the radius of H atom in HF, HCl, HBr, and HCN are, respectively, 0.55±0.07, 0.74±0.08, 0.80±0.11, and 0.93±0.07 Å. The radii found for HF, HCl, and HBr show a strong inverse correlation with the dipole moment of the HX. From this correlation the radius of H atom in HI is estimated to be 0.90±0.11 Å. By extrapolating to zero dipole moment, the van der Waals radius of H atom is determined to be 1.0±0.1 Å, reasonably close to the value proposed by Pauling, 1.2 Å